The invention relates to a mobile communication system comprising a mobile data unit acting via a mobile communication network as a remote workstation in a data network; a mobile exchange and; means for establishing a data connection between the mobile data unit and the mobile exchange.
Mobile communication systems have been developed as there have been a need to free people to leave their desktop telephone terminals and a need for others to reach them even when they are outside a specified location. As automation begins to be an integral part of the working environment, people outside offices wish to operate computers everywhere and make connections from any one location to another. The development of mobile communication systems offering voice services in the direction of data services thus seems to be inevitable.
Computer technology makes it possible to produce lightweight truly portable devices with improved processing power, storage capacity and user friendliness. This evolution of computers has made it technically and economically feasible to offer mobile data services for moving people. In such a case, the user is most likely to possess a mobile telephone terminal for voice communication, so the best way to provide data communication is through the mobile telephone system in much the same way as conventional telephone lines are used for data communication by using modems.
The deployment of digital mobile communication systems, such as the Pan-European mobile radio system GSM, means a break-through when mobile data communication is to be supported in general-purpose cellular networks. As the GSM is fully digital and applies the general principles of ISDN (Integrated Services Data Network), it is inherently capable of carrying data. From the data networking point of view, the GSM does not represent a dedicated data communication network but an access network. In other words, data communication via the GSM is intended to provide access to actual data networks.
The GSM network offers a wide range of services to subscribers. In addition to speech and emergency call services, the GSM network supports all variations of low-speed data communication services offered within telecommunication today. The only restriction is set by the capacity of the radio interface, which restricts the data rate to 9.6 kbit/s.
It is thus also possible to use the GSM system to connect a remote workstation to a desired data communication network, such as a Local Area Network (LAN). The remote workstation is usually a conventional workstation (PC) connected to the data interface of a mobile unit (mobile phone). The remote terminal may thus transmit data via the radio path with a data modem provided in association with the mobile exchange and further by means of a modem connection, e.g. through a public telephone network with a second data modem and a data terminal equipment connected to it. This second modem is usually attached to a computer connected to a LAN. This computer is used for enabling remote access to the LAN. It is usually called an Access Server. The access server has several data communication ports to which modems and a software enabling some kind of remote access are connected. Correspondingly, the remote workstation necessarily includes of has access to software in order that it is able to communicate with the access server software.
However, the above-described way of connecting a remote workstation via a mobile communication system to a data network has a few disadvantages. First, for instance, the GSM radio path enables a 9.6-kbit/s transmission rate and an excellent bit error rate of the order of 10.sup.-8. However, the connection is extended between the mobile communication network and the destination data network by means of a modem connection switched via a public telephone network. The maximum transmission rate of this kind of modem connection is usually 2.4 kbit/s, and its bit error rate is on the order of about 10.sup.-4 to 10.sup.-5. The entire connection will thus have the same transmission rate and bit error rate values, which are clearly inferior to those the GSM network, for instance, is able to offer. Second, the prior art method is not sufficiently efficient from the point of view of the radio path, as it is necessary to use a circuit-switched connection in the mobile communication network and keep the radio resources allocated throughout the LAN session, even during silent periods when there is no kind of communication.